1. Field of the Invention
The present invention relates to a passenger protecting apparatus, which inflates an air bag for protecting the passenger in an instant, when a vehicle has an accident such as a collision. More specifically, the present invention relates to a controlling unit of a squib for inflating an air bag. A "squib" is herein defined as a detonator for inflating an air bag and/or for tightening the seat belt, in this specification and Claims.
2. Description of the Prior Art
FIG. 8 shows a block diagram of a controlling unit of a squib, in the prior art, of a squib in such a passenger protecting apparatus.
An ignition switch 102, a DC/DC converter 103, a diode 104 for counter-current prevention, a first switching transistor 106 (first switching circuit), a squib 107, a second transistor 108 (second switching circuit) are connected in series between both of the terminals of a battery 101. The line connecting the diode 104 and the first switching transistor 106 is connected through a back up capacitor 105 with large capacity to the ground line.
In a collision, first and second acceleration sensors 109,111 generate acceleration signals. The acceleration signal from the first acceleration sensor 109 is provided to a collision judging means 110, and the acceleration signal from the second acceleration sensor 111 is provided to a comparing means 112. When the acceleration signal from the second acceleration sensor 111 exceeds a standard value, a high level signal is provided to an input terminal of an AND gate means 113 and to the collision judging means 110 as a switch signal.
The procedure of the collision judging algorithm in the collision judging means 110 begins at the moment, when a trigger signal, which corresponds to the standing up edge of the high level signal, is given. It estimates the accident whether the accident is so grave that it leads to an injury of the passenger(s). When it estimates that the accident can lead to a grave injury of the passenger(s), the collision judging means 110 supplies a high level signal to the other input terminal of the AND gate means 113.
The base terminal of the first switching transistor 106 is connected with the output terminal of the AND gate means 113 through an inverter 114, and the base terminal of the second switching transistor 108 is connected with the output terminal of the AND gate means 113 directly.
When the accident is estimated to be grave, the AND gate means receives high level signals from the collision judging means 110 and comparing means 112 simultaneously. As a result, the first and second switching transistors 106,108 turn on. The back up capacitor supplies the electric energy stored therein to the squib 107, then the squib actuates the air bag to inflate.
In the aforementioned passenger protecting apparatus, only one AND gate means 113 is used, and both switching transistors 106,108 are driven, depending on the output of the AND gate means.
There is a problem in constructing the controlling unit by a micro computer containing a CPU, and a soft ware program equivalent to the collision judging unit 110, the AND gate 113, the inverter and the comparing means 112.
When the output of the AND gate means becomes to a high level, due to malfunction in the soft ware program or due to a false signal caused by external noise, the first and second switching transistors connected to the both sides of the squib turn on simultaneously. This can lead to an erroneous operation of the squib.
FIG. 9 is a block diagram of another example of a controlling unit of a squib in a passenger protecting apparatus that is disclosed in a Japanese Patent Application, which has not yet been published.
The controlling unit comprises a controlling unit for a front air bag 201 (it is called also as a pre-tensioned unit), a controlling unit for a side air bag at the conductor's seat 202 and a controlling unit for a side air bag at the seat next to the driver 203, which communicate to each other using a multi-superposition communication system, using the power supply wire as a signal line.
At first, the controller unit for the front air bag is explained.
First, second and third voltage increasing circuits 206, 207, 208 convert the input voltage, which is supplied from a battery 204 through an ignition switch 205, to a higher voltage and charge a first, second and third back up capacitor 209, 210, 211, which are respectively connected.
The input terminals of a first, second and third switching circuit 212, 213, 214 are connected respectively with the output terminal of the corresponding first, second and third voltage increasing circuits 206, 207, 208, and their output terminals are connected respectively with a corresponding squib 215, 216, 217.
When the ignition switch 205 is put on, the first, second and third back up capacitor 209, 210, 211 are charged from the battery 204 through the first, second and third voltage increasing circuits 206, 207, 208, and a micro computer 220 in the controlling unit for front air bag 201 starts its procedure. Simultaneously, the voltage regulating circuit 223 begins to supply electric power to the controlling units for the side air bag at the driver's seat 202 and the controlling unit for side air bag at the seat next to the driver' seat 203.
When an igniting signal is provided to the input terminal of one of the first, second and third switching circuits 212, 213, 214 from the micro computer 220, an ignition current from the corresponding back up capacitor 209, 210, 211 flows through the corresponding first, second and third squibs 215, 216, 217.
Reference numeral 218 denotes a mechanical acceleration sensor, which is connected with the first squib 215 in series and turns on when an acceleration over a predetermined value is detected. On the other hand, the longitudinal direction acceleration sensor 219 is an electric acceleration sensor, which detects the longitudinal acceleration at an collision of vehicle.
Reference numeral 220 denotes a micro computer, having a collision judging function. It estimates the accident as to whether it is grave or not, on the basis of the acceleration signal from the longitudinal acceleration sensor 219. When it estimates that the accident is grave, it turns on the first switching circuit 212. Hence, the charge stored in the first back up capacitor 209 flows as an ignition current through the first squib 215 and the mechanical acceleration sensor 218, which are connected in series. As a result, the front air bag for a front collision of vehicle is inflated, or the pre-tensioned unit is actuated. In this manner, the air bag and so like is inflated protecting the passenger(s) at the front collision of vehicle.
The controlling unit for the side air bag at the driver's seat 202 comprises of a first transverse acceleration sensor 230, a micro computer 231, an acceleration switch 232, a second sending circuit 233, a resistor 234 and a second receiving circuit 235. On the other hand, The controlling unit for the side air bag at the seat next to the driver's seat 203 comprises a second transverse acceleration sensor 240, a micro computer 241, an acceleration switch 242, a third sending circuit 243, a resistor 244 and a third receiving circuit 245. The corresponding components in both of the units are identical.
The transverse acceleration sensors 230, 240 have an identical structure as the longitudinal acceleration sensor 219, however, they are configured so as to detect the acceleration in the direction differed 90 degrees from the detection direction of the longitudinal acceleration sensor 219, namely they detect the acceleration in the transverse direction of vehicle. They provide their outputs to the micro computer 231, 241, respectively.
The micro computer 231, 241 have a collision judging functions as the micro computer 220 has, and estimate the accident on the basis of the acceleration signals provided from the second or third transverse acceleration sensors 230, 240 and the switch signal provided from the acceleration switches 232, 242.
The voltage regulating circuit 223 supplies a regulated voltage through the resistor 224 to the controlling units for the side air bag at the driver's seat 202 and for the side back at the seat next to the driver's seat 203.
A signal demand signal from the micro computer 220 to the controlling units for the side air bag at the driver's seat 202 or to the controlling unit for the side back at the seat next to the driver's seat 203 is provide to the first sending circuit 225 via a signal line X. The first sending circuit 225 superimposes it on the power supply line A.
On the other hand, when the micro computer 231 in the controlling units for the side air bag at the driver's seat 202 estimates that the accident is grave, on the basis of the switch signal from the first acceleration switch 232 and the acceleration signal from the first transverse acceleration sensor 230, it sends a corresponding signal, as a responding signal to the signal demanding signal from the micro computer 220, through the second sending circuit 233, the resistor 234 and the power supply line A, which are connected in series.
In the same manner, when the micro computer 241 in the controlling units for the side air bag at the driver's seat 203 estimates that the accident is grave, on the basis of the switch signal from the second acceleration switch 242 and the acceleration signal from the second transverse acceleration sensor 240, it sends a corresponding signal, as a responding signal to the signal demanding signal from the micro computer 220, through the third sending circuit 243, the resistor 244 and the power supply line A, which are connected in series.
The first receiving circuit 226 receives the responding signal from the controlling unit for the side air bag at the driver's seat 202 or from the controlling unit for the side air bag at the seat next to the driver's seat 203 through the power supply line, which functions here as a communication line. And it sends the responding signal to the micro computer 220 through a communication line Z.
When the micro computer 220 receives a signal, indicating that the accident is grave, from the micro computer 231 or 241 through the communication line Z, it actuates the corresponding second or third switch circuit 213, 241 to turn on. Hence, the charge stored in the second or third back up capacitor 210, 211 flows through the second or third squid 216, 217. As a result, the side air bag at the driver's seat of at the seat next to the driver's seat is inflated. In this manner, the air bag is inflated for protecting the passenger from the side collision of vehicle.
The rigidity of an old type vehicle is strong in the longitudinal direction, and is relatively weak in the transverse direction of vehicle. Accordingly, the controlling unit for a front collision 201 is located at the intermediate portion of the driver's seat and the seat next to the driver's seat. And the controlling units for a side collision 202, 203 are located separately at a lower portion of the center pillars beside the driver's seat and the seat next to the driver's seat. This is in order to assure the protection of the passenger from both front and side collisions. Due to this structure, fabrication and installing costs are rather large.
Recently, however, vehicles have the improvement of having high rigidity against external forces in the transverse direction. Thus the necessity to arrange the controlling units separately has decreased.